Flood Regionalization

Project Objectives

The overall objective of this project is to develop regional peak discharge relations for ungaged drainage basins in New Jersey by evaluating the stream gage data collected from the cooperative New Jersey gage network. The specific study objectives are:

Develop regional peak discharge equations for non-tidal streams in New Jersey that are not heavily regulated by reservoirs for the 2-, 5-, 10-, 25-, 50-, 100- and 500-year recurrence intervals for four (4) to five (5) regions in the State.

Develop a web page to automate the determination of flood magnitude and frequency for existing gaged sites and at ungaged sites.

Statement of Problem

A method of estimating the flood magnitude and frequency of ungaged streams in New Jersey is an important need of engineers and planners. The potential for flooding and an increase in the potential damage due to flooding has increased in many areas as the population of New Jersey has grown from about 5 million people in 1950 to over 8 million people in 2000. The population increase and associated spread of development has increased the number of areas that are vulnerable to flooding. Development has in some areas produced greater runoff due to increased amounts of impervious surfaces resulting in increased flooding down stream. Planning for future land use and infrastructure for small drainage basins that are vulnerable to high intensity storms requires flow information to develop flood frequency curves. Existing methods for estimating flood magnitude and frequency for ungaged streams tend to have a geographic bias. The previous flood estimating equations were developed by the USGS and published as NJDEP Special Report 38, published in 1974.

Strategy and Approach

The project will use data from the various gaging networks in New Jersey, and portions of the gage networks of nearby Pennsylvania, New York, and Delaware to develop a database for analysis. A minimum of 10 years of flood records at a station is required for analysis. The data from New Jersey streams, as well as from nearby states will be grouped into similar geographic regions in order to develop four or five regional relations to minimize geographic bias. Work on the project will be divided into 2 phases. The first phase will cover development and publication of new regional equations. The second phase will involve development and documentation of a web site to automate the determination of flood magnitude and frequency for ungaged sites.